In 3GPP (3rd Generation Partnership Project), LTE-A (LTE-Advanced) is under study as the next communication method after LTE (Long-Term Evolution (3rd generation)). In LTE-A, in order to achieve communication at a higher speed than LTE, study is being conducted regarding communication using a 100-MHz frequency band that is broader than the 20-MHz frequency band used in LTE. However, because of existing frequency spectrum allocations to various applications, it is difficult to achieve a continuous allocation of frequency spectrum for LTE-A. It is also desirable to maintain compatibility with LTE as much as possible. Given these objectives, a proposal has been made for achieving a maximum 100-MHz frequency band by communicating on a plurality of frequency bands having widths that are 20 MHz or narrower, so as to perform carrier aggregation that achieves both high speed and high-capacity communication. This proposal has been agreed upon at a conference (3GPP RAN1#53b, refer to Non-Patent Document 1). In this carrier aggregation, carriers (frequency bands) up to 20 MHz are referred to as component carriers (CCs). There are future plans to establish detailed specifications with regard to signaling, channel placement, and mapping and the like in carrier aggregation.
In placing control channels on a downlink, a method that can be envisioned for maintaining compatibility with LTE is that of placing a PCFICH (Physical Control Format Indicator Channel), a PHICH (Physical Hybrid Automatic Repeat Request Indicator Channel, HARQ indicator channel), or PDCCH (Physical Downlink Control Channel) in each component carrier channel as the control channel. In this carrier aggregation method, if it is not established beforehand which component carrier is to be used to transmit control information, it is necessary for the terminal device to monitor a plurality of component carriers at the same time. It is therefore necessary for the receiving unit of the terminal device to wait for signals corresponding to frequency bands of a plurality of component carriers. For this reason, the power consumption of the terminal device increases in comparison with the case of waiting for a signal corresponding to frequency band of one component carrier.
In order to execute carrier aggregation, it is necessary to establish a new DCI (Downlink Control Information) format that sacrifices compatibility with LTE to some extent. When this is done, the control information for other channels is collected into one of the component carriers. By doing this, it is possible to reduce the amount of feedback of the acknowledge (ACKnowledge; ACK) signal and not-acknowledge (Not-ACKnowledge; NACK) signal in HARQ. In the case of using this method, since it is sufficient that a terminal device in the waiting state monitor only the one component carrier in which control information is stored, the power consumption of the terminal device can be reduced. Non-Patent Document 2 proposes, based on this method, a technique that uses Semi-Dynamic Triggering PDCCH to notify of component carriers which are aggregated. This Semi-Dynamic Triggering PDCCH includes a set of component carriers that are activated in the next subframe, and information regarding the effective period of this activation. An LTE-A terminal device that receives the Semi-Dynamic Triggering PDCCH can then monitor just the component carrier set that has been activated, up until the effective period, thereby enabling a reduction of the power consumption.
Non-Patent Document 3 indicates that, because communication on a plurality of component carriers increases the power consumption, it is desirable to communicate on one component carrier as much as possible.
Non-Patent Document 4 discloses an anchor carrier, which is a component carrier used as the basis for communicating control signals and the like.